The present invention relates to a magnet article for attracting foreign matters such as magnetically attractable matters in the shape of nail, wire, needle, power, etc. in the stomachs of ruminants such as cows.
Typical ruminants such as cows grazing in a field have ruminant stomachs and tend to swallow grass or hay without sufficient mastication. Accordingly, if there are nails, needles, wires, magnetic powders, etc. in the feeds, they would be swallowed together with the feeds into the rumen and the second stomach. If this happens, the stomach is damaged, causing various troubles such as gastritis, dyspepsia, etc. As a result, the cows die in an extreme case.
To prevent such incidents, the feeds supplied to the cows are usually examined to detect metallic foreign matters, particularly iron articles, and the fields are also examined to detect such metallic foreign matters. Despite such examination, it has been impossible to completely prevent the cows from swallowing metallic foreign matters. Accordingly, rod-shaped permanent magnets are conventionally swallowed into the second stomachs of the cows in order to attract magnetically attractable matters accidentally taken by the cows. This procedures prevent the magnetically attractable matters from sticking the gastric mucosae of the cows.
Conventionally used as magnet articles for attracting foreign matters in the stomachs are rod-shaped Alnico magnets having magnetic poles on both end surfaces. However, since these rod-shaped Alnico magnets have magnetic poles on both ends, they do not have an attraction force in their middle portions. As a result, metal pieces such as nails, needles, etc. are attracted predominantly to both ends of the rod-shaped Alnico magnets, and rather cause damage to the gastric mucosae. In addition, since the ends of Alnico magnets have round surfaces to protect the gastric mucosae, metal pieces attracted to the Alnico magnets are extremely unstable, so that the attraction force of the magnets cannot fully be utilized.
There are also rod-shaped Alnico magnets having a plurality of magnetic poles along their cylindrical surfaces, for instance, eight magnetic poles extending longitudinally on their cylindrical surfaces. These rod-shaped magnets show higher attraction force than those having a pair of magnetic poles on both ends. However, they do not have sufficiently high surface magnetic flux density due to small coercive forces thereof. In addition, since demagnetization takes place due to the contact of metal pieces attracted to the rod-shaped magnets, the magnets fail to keep the metal pieces attracted thereto, permitting the metal pieces to move into the subsequent stomachs.
To obviate such problems, proposals have been made to provide a magnet article for attracting foreign matters in the stomach, which comprises a plurality of disc-shaped magnet members having opposing magnetic poles on both end surfaces and arranged coaxially such that the magnetic poles having the same polarity face each other between the adjacent permanent magnets (for instance, Japanese Utility Model Publication No. 57-53550 and Japanese Utility Model Laid-Open No. 60-61703).
These magnet articles have a plurality of magnetic poles in their intermediate portions in addition to their end portions, so that even elongated metal pieces can be attracted thereto along their lengths. As a result, the gastric mucosae are prevented from being sticked by metal pieces.
However, those proposed by the above Japanese references are made of ferrite magnets, failing to show sufficient magnetic forces. Specifically, these magnet articles show surface magnetic flux densities of only 1600-1800 G, which make the magnet articles unable to attract and keep elongated metal pieces completely along their lengths. As a result, it is impossible to keep the elongated metal pieces from sticking the gastric mucosae completely.
In addition, since porous ferrite magnets are exposed to a gastric juice in these magnet articles, they are eroded by the gastric juice. As a result, their service lives are relatively short.
Incidentally, even if the ferrite magnets are replaced by the Alnico magnets, the service lives of the magnet articles cannot be sufficiently elongated, and their fabrication becomes rather complicated. In addition, since the Alnico magnets show smaller coercive forces than the ferrite magnets, the magnet articles constituted by the Alnico magnets cannot show as high magnetic forces as the ferrite magnets.